High power radiation emitter device and heat dissipating package for electronic components

ABSTRACT

The electronic component package ( 10 ) of the present invention includes a sealed chamber; a liquid or gel ( 20 ) contained in the sealed chamber; at least one electronic component ( 12 ) disposed in the sealed chamber in physical and thermal contact with the liquid or gel ( 20 ); and at least one electrical conductor electrically coupled to the electronic component and extending out of the sealed chamber. The electronic component(s) ( 12 ) may include any one or combination of a radiation emitter, a thermal or optical sensor, a resistor, and a microprocessor or other semiconductor component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 09/835,238 filed on Apr. 13, 2001, now U.S. Pat. No. 6,639,360,which claims benefit of U.S. Provisional Application No. 60/265,487filed on Jan. 31, 2001.

BACKGROUND OF THE INVENTION

The present invention generally relates to radiation emitter assembliessuch as, for example, light emitting diode (LED) packages and to heatdissipating packages for electronic components.

Radiation emitters, particularly optical radiation emitters, are used ina wide variety of commercial and industrial products and systems andaccordingly come in many forms and packages. As used herein, the term“optical radiation emitter” includes all emitter devices that emitvisible light, near infrared (IR) radiation, and ultraviolet (UV)radiation. Such optical radiation emitters may be photoluminescent,electroluminescent, or other solid state emitter. Photoluminescentsources include phosphorescent and fluorescent sources. Fluorescentsources include phosphors and fluorescent dyes, pigments, crystals,substrates, coatings, and other materials.

Electroluminescent sources include semiconductor optical radiationemitters and other devices that emit optical radiation in response toelectrical excitation. Semiconductor optical radiation emitters includelight emitting diode (LED) chips, light emitting polymers (LEPs),organic light emitting devices (OLEDs), polymer light emitting devices(PLEDs), etc.

Semiconductor optical emitter components, particularly LED devices, havebecome commonplace in a wide variety of consumer and industrialoptoelectronic applications. Other types of semiconductor opticalemitter components, including OLEDs, LEPs, and the like, may also bepackaged in discrete components suitable as substitutes for conventionalinorganic LEDs in many of these applications.

Visible LED components of all colors are used alone or in small clustersas status indicators on such products as computer monitors, coffeemakers, stereo receivers, CD players, VCRs, and the like. Suchindicators are also found in a diversity of systems such as instrumentpanels in aircraft, trains, ships, cars, trucks, minivans and sportutility vehicles, etc. Addressable arrays containing hundreds orthousands of visible LED components are found in moving-message displayssuch as those found in many airports and stock market trading centersand also as high brightness large-area outdoor television screens foundin many sports complexes and on some urban billboards.

Amber, red, and red-orange emitting visible LEDs are used in arrays ofup to 100 components in visual signaling systems such as vehicle centerhigh mounted stop lamps (CHMSLs), brake lamps, exterior turn signals andhazard flashers, exterior signaling mirrors, and for roadwayconstruction hazard markers. Amber, red, and blue-green emitting visibleLEDs are increasingly being used in much larger arrays of up to 300components as stop/slow/go lights at intersections in urban and suburbanintersections.

Multi-color combinations of pluralities of visible colored LEDs arebeing used as the source of projected white light for illumination inbinary-complementary and ternary RGB illuminators. Such illuminators areuseful as vehicle or aircraft maplights, for example, or as vehicle oraircraft reading or courtesy lights, cargo lights, license plateilluminators, backup lights, and exterior mirror puddle lights. Otherpertinent uses include portable flashlights and other illuminatorapplications where rugged, compact, lightweight, high efficiency,long-life, low voltage sources of white illumination are needed.Phosphor-enhanced “white” LEDs may also be used in some of theseinstances as illuminators.

IR emitting LEDs are being used for remote control and communication insuch devices as VCR, TV, CD, and other audio-visual remote controlunits. Similarly, high intensity IR-emitting LEDs are being used forcommunication between IRDA devices such as desktop, laptop and palmtopcomputers; PDAs (personal digital assistants); and computer peripheralssuch as printers, network adapters, pointing devices (“mice,”trackballs, etc.), keyboards, and other computers. IR LED emitters andIR receivers also serve as sensors for proximity or presence inindustrial control systems, for location or orientation within suchopto-electronic devices such as pointing devices and optical encoders,and as read heads in such systems as barcode scanners. IR LED emittersmay also be used in a night vision system for automobiles.

Blue, violet, and UV emitting LEDs and LED lasers are being usedextensively for data storage and retrieval applications such as readingand writing to high-density optical storage disks.

Performance and reliability of LED components, chips, and systems areheavily influenced by the thermal performance of those components,chips, and systems, and by ambient temperature. Elevated operatingtemperatures simultaneously reduce the emission efficiency of LEDs andincrease the probability of failure in most conditions. This elevatedtemperature may be the result of high system thermal resistance actingin concert with internal LED power dissipation and may also be theresult of high ambient operating temperature or other influence.Regardless of the cause, LED efficiency and reliability are normaladversely affected by increases in temperature. Thus, it is advantageousto minimize temperature rise of LED components, chips, and systemsattributable to internal power dissipation during operation. This can beaccomplished by reducing the conductive, convective, and radiativethermal resistance between the LED chip and ambient environment, such asby optimizing the materials and construction of the packaged devicecontaining the LED chip. These methods, as applicable tomass-solderable, auto-insertable, and other discrete LED components, aredisclosed in commonly assigned U.S. Pat. No. 6,335,548, entitled“SEMICONDUCTOR RADIATION EMITTER PACKAGE,” filed on Oct. 22, 1999, byJohn K. Roberts et al., and published PCT International Publication No.WO 00/55914.

For high power LED systems and high power density LED systems, systemthermal performance is especially critical. LED illuminators and highpower signal lights generating more than ten lumens (or more than onewatt of power dissipation) are examples of systems which can benefitfrom improved thermal performance, especially if package area/volumemust be minimized (increasing power density).

To limit the operational temperature of the LED, the power that isallowed to be dissipated through the LED is typically limited. To limitthe dissipated power, however, the current that may be passed throughthe LED must be limited, which in turn limits the emitted flux of theLED since the emitted flux is typically proportional to the electricalcurrent passed through the LED.

Other fundamental properties of LEDs place further restrictions on theuseful operational temperature change ΔT. Semiconductor LEDs, includingIR, visible, and UV emitters, emit light via the physical mechanism ofelectro-luminescence. Their emission is characteristic of the band gapof the materials from which they are composed and their quantumefficiency varies inversely with their internal temperature. An increasein LED chip temperature results in a corresponding decrease in theiremission efficiency. This effect is quite significant for all commontypes of LEDs for visible, UV, and IR emission. Commonly, a 1° C.increase (ΔT) in chip temperature typically results in up to a 1 percentreduction in useful radiation and up to a 0.1 nm shift in the peakwavelength of the emission, assuming operation at a constant power.Thus, a ΔT of 40° C. can result in up to a 40 percent reduction inemitted flux and a 4 nm shift in peak wavelength.

From the preceding discussion, it can be seen that to avoid thermaldamage and achieve optimal LED emission performance, it is veryimportant to minimize the ΔT experienced by the LED device chip andpackage during operation. This may be achieved by limiting power orreducing thermal resistance.

Limiting LED power, of course, is antithetical to the purpose of highpower LEDs, i.e., to produce more useful radiation. Generating higherflux with an LED generally requires higher current (and therefore higherpower). Most prior art devices, however, exhibit relatively high thermalresistance from their semiconductor radiation emitter to ambient and arecompelled to limit power dissipation in order to avoid internal damage.Thus, the best 5 mm T-1¾ THD packages are limited to about 110 mWcontinuous power dissipation at 25° C. ambient temperature.

An additional problem faced by designers of conventional LED devices isthat the wire bond used to join one of the LED leads to the LED chip canbreak or lose contact with the lead or the chip. Such failure can occur,for example, due to shear forces that are transferred to the wire bondthrough the encapsulant or thermal expansion/contraction of theencapsulant around the wire bond.

The other forms of radiation emitters mentioned above also experienceperformance degradation, damage, increased failure probability oraccelerated decay if exposed to excessive operating temperatures.

Consequently, it is desirable to provide a radiation emitter device thathas a higher emission output than conventional LED devices while beingless susceptible to failure due to a break in the wire bond contact orother defect that may be caused by excessive operating temperatures.

Similar heat dissipation problems exist with respect to other electroniccomponents. For example, large heat sinks are often attached tomicroprocessors of the type used in personal computers. Accordingly, animproved heat dissipation package for such electronic components isdesirable.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a relatively highpower and high power density radiation emitter device capable of highradiant flux and/or luminous flux emission. It is a further aspect ofthe present invention to provide a radiation emitter device exhibitingrelatively low temperature rise due to internal power dissipation andincreased reliability by virtue of relatively low thermal resistance. Toachieve these and other aspects and advantages in accordance with oneembodiment of the present invention, the radiation emitting device ofthe present invention comprises a sealed chamber; one or more liquids orgels contained in the sealed chamber; an electroluminescent emitter thatemits optical radiation in response to an electrical signal, theelectroluminescent emitter is disposed in the sealed chamber in physicaland thermal contact with one of the liquids or gels; and first andsecond electrical conductors electrically coupled to theelectroluminescent emitter for energizing the electroluminescentemitter. A portion of the structure defining the sealed chamber may bepartially transparent to allow the radiation to enter or exit.

It is another aspect of the present invention to provide a package forelectronic components having improved heat dissipation characteristics.To achieve these and other aspects and advantages, the electroniccomponent package comprises first and second substrates sealed togetherand spaced apart to define a sealed chamber, one or more liquids or gelscontained in the sealed chamber, and at least one electronic componentdisposed in the sealed chamber and thermal contact with one of theliquids or gels. According to one embodiment, the at least oneelectronic component includes a semi-conductor electronic component.According to another embodiment of the invention, the first substrate isa printed circuit board.

According to another embodiment, an optical radiation emitting devicecomprises: a sealed chamber; a fluid intermediary material contained inthe sealed chamber and having a refractive index greater than 1.0; anelectroluminescent emitter that emits optical radiation in response toan electrical signal, the electroluminescent emitter disposed in thesealed chamber in physical and thermal contact with the fluidintermediary material; and first and second electrical conductorselectrically coupled to the electroluminescent emitter for energizingthe electroluminescent emitter.

According to another embodiment, an optical radiation emitting devicecomprises: a semiconductor radiation emitter that emits opticalradiation in response to an electrical signal; a protective barrier forprotecting the semiconductor radiation emitter, the protective barriercomprises a material that substantially maintains its in-band opticalproperties over time; and first and second electrical conductorselectrically coupled to the semiconductor radiation emitter forenergizing the semiconductor radiation emitter.

These and other features, advantages, and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a top elevational view of a radiation emitting deviceconstructed in accordance with a first embodiment of the presentinvention;

FIG. 2 is a perspective view of the radiation emitting device of firstembodiment of the present invention;

FIG. 3A is a cross-sectional view taken along line 3–3′ of the radiationemitting device shown in FIG. 1;

FIG. 3B is a cross-sectional view of an alternative embodiment of thedevice shown in FIG. 1;

FIG. 3C is a cross-sectional view of an alternative embodiment of thedevice shown in FIG. 1;

FIG. 4 is a cross-sectional view of a radiation emitter deviceconstructed in accordance with a second embodiment of the presentinvention;

FIG. 5 is a cross-sectional view of a radiation emitter deviceconstructed in accordance with a third embodiment of the presentinvention;

FIG. 6A is a cross-sectional view of a radiation emitter deviceconstructed in accordance with a first variation of a fourth embodimentof the present invention;

FIG. 6B is a cross-sectional view of a radiation emitter deviceconstructed in accordance with a second variation of a fourth embodimentof the present invention;

FIG. 7 is a top view of a radiation emitter device constructed inaccordance with a fifth embodiment of the present invention;

FIG. 8 is a perspective view of a vehicle headlamp assembly constructedin accordance with the present invention;

FIG. 9 is a schematic diagram of an electrical circuit that may beprovided in one or more of the above embodiments;

FIG. 10 is a top view of an initial package subassembly in accordancewith a sixth embodiment of the present invention;

FIG. 11 is a top view of a finished package assembly constructed inaccordance with the sixth embodiment of the present invention;

FIG. 12 is a graph illustrating the illuminance as a function of powerfor the package assembly shown in FIG. 11 with the chamber filled withliquid and with the sealed chamber not filled with any liquid;

FIG. 13 is a graph of the relative spectral irradiance as a function ofwavelength obtained for the package assembly shown in FIG. 11 with thechamber not filled with any liquid for various power levels;

FIG. 14 is a graph of the relative spectral irradiance as a function ofwavelength obtained for the package assembly shown in FIG. 11 with thechamber filled with liquid for various power levels;

FIG. 15 is a cross-sectional view of an alternative embodiment of thedevice shown in FIG. 1;

FIG. 16 is a plan view of a subassembly of the device shown in FIG. 15;

FIG. 17A is a cross-sectional view of an alternative embodiment of thedevice shown in FIG. 1;

FIG. 17B is a cross-sectional view of an alternative embodiment of thedevice shown in FIG. 1; and

FIG. 18 is a cross-sectional view of an electronic component packageassembly constructed in accordance with an alternate embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferredembodiments of the invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numeralswill be used throughout the drawings to refer to the same or like parts.

For purposes of description herein, the terms “upper,” “lower,” “right,”“left,” “rear,” “front,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the invention as viewed by a personlooking directly at the radiation emitting source along the principaloptical axis of the source. However, it is to be understood that theinvention may assume various alternative orientations, except whereexpressly specified to the contrary. It is also to be understood thatthe specific device illustrated in the attached drawings and describedin the following specification is simply an exemplary embodiment of theinventive concepts defined in the appended claims. Hence, specificdimensions, proportions, and other physical characteristics relating tothe embodiment disclosed herein are not to be considered as limiting,unless the claims expressly state otherwise.

Several embodiments of the present invention generally relate to animproved optical radiation-emitting device useful in both high and lowpower applications. Such embodiments of the present invention areparticularly well suited for use in limited power applications such asvehicles, portable lamps, and specialty lighting. By vehicles, we meanover-land vehicles, watercraft, aircraft and manned spacecraft,including but not limited to automobiles, trucks, vans, buses,recreational vehicles (RVs), bicycles, motorcycles and mopeds, motorizedcarts, electric cars, electric carts, electric bicycles, ships, boats,hovercraft, submarines, airplanes, helicopters, space stations,shuttlecraft and the like. By portable lamps, we mean camping lanterns,head or helmet-mounted lamps such as for mining, mountaineering, andspelunking, hand-held flashlights and the like. By specialty lighting wemean emergency lighting activated during power failures, fires or smokeaccumulations in buildings, microscope stage illuminators, billboardfront-lighting, backlighting for signs, etc. The light emitting assemblyof the present invention may be used as either an illuminator or anindicator. Examples of some of the applications in which the presentinvention may be utilized, are disclosed in commonly assigned PCTInternational Publication No. WO 00/55685 entitled “INDICATORS ANDILLUMINATORS USING A SEMICONDUCTOR RADIATION EMITTER PACKAGE,” by JohnK. Roberts et al.

Some of the embodiments of the present invention provide a highlyreliable, low-voltage, long-lived, light source for vehicles, portablelighting, and specialty lighting capable of producing white light withsufficient luminous intensity to illuminate subjects of interest wellenough to be seen and to have sufficient apparent color and contrast soas to be readily identifiable. Several of the radiation emitter devicesof the present invention may be well suited for use with AC or DC powersources, pulse-width modulated DC power sources, and electronic controlsystems. The radiation emitting devices of the present invention mayfurther be used to emit light of various colors and/or to emitnon-visible radiation such as IR and UV radiation.

As used herein, the terms “radiation emitter” and “radiation emittingdevice” shall include any structure that generates and emits optical ornon-optical radiation, while the term “optical radiation emitter” or“optical radiation emitting device” includes those radiation emittersthat emit optical radiation, which includes visible light, near infrared(IR) radiation, and/or ultraviolet (UV) radiation. As noted above,optical radiation emitters may include electroluminescent sources orother solid-state sources and/or photoluminescent or other sources. Oneform of electroluminescent source includes semiconductor opticalradiation emitters. For purposes of the present invention,“semiconductor optical radiation emitters” comprise any semiconductorcomponent or material that emits electromagnetic radiation having awavelength between 100 nm and 2000 nm by the physical mechanism ofelectroluminescence, upon passage of electrical current through thecomponent or material. The principal function of a semiconductor opticalradiation emitter within the present invention is the conversion ofconducted electrical power to radiated optical power. A semiconductoroptical radiation emitter may include a typical IR, visible or UV LEDchip or die well known in the art and used in a wide variety of priorart devices, or it may include any alternate form of semiconductoroptical radiation emitter as described below.

Alternate forms of semiconductor optical radiation emitters which may beused in the present invention are light emitting polymers (LEPs),polymer light emitting diodes (PLEDs), organic light emitting diodes(OLEDs) and the like. Such materials and optoelectronic structures madefrom them are electrically similar to traditional inorganic LEDs, butrely on organic compositions such as derivatives of the conductivepolymer polyaniline for electroluminescence. Such semiconductor opticalradiation emitters are relatively new, but may be obtained from sourcessuch as Cambridge Display Technology, Ltd. of Cambridge, Mass. and fromUniax of Santa Barbara, Calif.

For brevity, the term semiconductor optical radiation emitter may besubstituted with the term LED or the alternate forms of emittersdescribed above or known in the art. Examples of emitters suitable forthe present invention include varieties of LED chips with associatedconductive pads for electrical attachment and that are emissiveprincipally at P—N or N—P junctions within doped inorganic compounds ofAlGaAs, AlInGaP, GaAs, GaP, InGaN, AlInGaN, GaN, SiC, ZnSe and the like.

LEDs are a preferred electroluminescent light source for use in theradiation emitting devices of the present invention because LEDs do notsuffer appreciable reliability or field-service life degradation whenmechanically or electronically switched on and off for millions ofcycles. The luminous intensity and illuminance from LEDs closelyapproximates a linear response function with respect to appliedelectrical current over a broad range of conditions, making control oftheir intensity a relatively simple matter. Finally, recent generationsof AlInGaP, AlGaAs, InGaN, AlInGaN, and GaN LEDs draw less electricalpower per lumen or candela of visible light produced than incandescentlamps, resulting in more cost-effective, compact, and lightweightilluminator wiring harnesses, fuses, connectors, batteries, generators,alternators, switches, electronic controls, and optics. A number ofexamples have previously been mentioned and are incorporated within thescope of the present invention, although it should be recognized thatthe present invention has obvious other applications beyond the specificones mentioned which do not deviate appreciably from the teachingsherein and therefore are included in the scope of this invention.

Another preferred radiation source that may be used in the inventivelight emitting assembly is a photoluminescent source. Photoluminescentsources produce visible light by partially absorbing visible orinvisible radiation and re-emitting visible radiation. Photoluminescentsources phosphorescent and fluorescent materials, which includefluorescent dyes, pigments, crystals, substrates, coatings, as well asphosphors. Such a fluorescent or phosphorescent material may be excitedby an LED or other radiation emitter and may be disposed within or onthe LED, or within or on a separate optical element, such as a lens ordiffuser that is not integral with an LED. Exemplary structures using afluorescent or phosphorescent source are described further below.

As explained in more detail below, the present invention exhibits asignificantly lower thermal resistance than conventional LED structuresby extracting heat from the LED chip(s) via all of the surfaces of theLED chip(s) simultaneously instead of from primarily only one surface asin typical prior art LED devices. More specifically, the radiationemitter package of the present invention provides a sealed chamber orcavity containing a liquid or gel surrounding the LED chips, the liquidor gel having a moderate to high thermal conductivity, a moderate tohigh convectivity, or both. A material that is “moderate to highlyconvective” is a material that is more effectively convective thaneither air or a conventional clear solid polymer such as epoxy orsilicone. “Effectively convective” means transporting substantialproportions of heat dissipated from a source by natural convection. TheLED chips may be mounted to a moderate to high thermal conductivityplate to which a transparent plate is sealed in spaced-apart relation todefine the sealed chamber or cavity. This combination is uniquelyeffective because heat is removed from large surfaces of the chip byconduction and by convective transport due to the natural convection ofthe liquid in the sealed chamber or cavity. Embodiments of the presentinvention are discussed below in connection with FIGS. 1–18. It will beappreciated that these embodiments are provided for purposes ofillustration only and are not limiting to the present invention.

FIGS. 1–3 show a radiation emitter device 10 constructed in accordancewith a first embodiment of the present invention. Device 10 includes oneor more radiation emitting sources 12, which are shown in FIG. 1 mountedto a first substrate 14. Although radiation emitters 12 are preferablyLED chips or dies, other forms of radiation emitters may be used. TheLED chips may be any conventional LED chip including those with verticaland lateral structure, transparent or absorbing substrate, electricallyconductive or insulating substrate, tapered sides, Truncated InvertedPyramid (TIP) construction, partial TIP construction, or flip chip, orother chip geometry, including LED chips utilizing AlGaAs, AlInGaP,GaAs, GaP, InGaN, AlInGaN, GaN, SiC, ZnSe and other inorganic compoundsemiconductor materials. The anode can be on the topmost surface of thechip, normally used for wirebond, and the cathode may be on the bottomof the chip, normally connected with die attach adhesive, solder oreutectic bonding. As with some InGaN/SiC LED chips, this polarity may bereversed such that the cathode is at the topside, normally used forwirebond and the anode is at the bottom, normally connected with dieattach adhesive, solder or eutectic bonding. Alternately, both anode andcathode may be topside of the chip as in a lateral type InGaN/sapphireLED chip structure, normally connected by wirebonding. Both contacts mayalso be at the bottom side of the chip in flip-chip configuration, andnormally attached with solder or die attach adhesive. LED chips suitablefor use in the present invention included are available from sourcessuch as Cree, AXTI, UOE, LumiLEDS and UEC and others. For purposes ofthis first embodiment, first substrate 14 may be made of anyelectrically conductive material, and preferably a material that hasrelatively high thermal conductivity. Preferably, first substrate 14 hasa thickness of 0.5 to 6.1 mm and is made of copper or aluminum. Asdescribed below with respect to other embodiments, the first substratemay alternately be made of electrically nonconductive material (such asa ceramic, PC board, passivated metal clad board, etc.). The firstsubstrate may also comprise all or a portion of or surface of anexternal cooling structure such as a heat sink or thermoelectric cooler.An optional submount made of silicon, silicon carbide, metal or otherlike materials, may be mounted between emitters 12 and first substrate14 to facilitate distribution of electrical power or to moderate thephysical properties of the emitters and the first substrate.

Radiation emitter assembly 10 further includes a second substrate 16serving as a protective barrier that is spaced apart from firstsubstrate 14. At least a portion of second substrate 16 through whichradiation is emitted from radiation emitters 12 is substantiallytransparent to some or all of the wavelengths of radiation emitted fromemitters 12. Alternatively, all of second substrate 16 may betransparent to the radiation emitted from radiation emitters 12 oralternatively transparent to all visible, IR, and/or UV radiation. Forexample, second substrate 16 may be made of a 0.5 to 6.1 mm glass coverplate. For some embodiments, this glass may be conventional soda-limefloat glass, and in others it may be fused silica glass, borosilicatefloat glass or other glass composition. Second substrate 16 may also bemade of tempered glass, an epoxy sheet, or transparent plastics that arealiphatic or olefinic in nature (e.g., polypropylene, polyethylene,dicylcopentadienes and polymethylpentenes). Such transparent aliphaticor olefinic plastics do not degrade when exposed to aprotic solventssuch as propylene carbonate, which is one possible liquid that may beused in the present invention. These transparent plastics also functionwell in solid-state systems that include pure solution-phase and partialsolution-phase electrolytes. These transparent plastics include: cyclicolefin copolymers such as TOPAS® available from Ticona, LLC of Summit,N.J. polymethylpentenes such as TPX™ manufactured by Mitsui;hydrogenated cyclo-olefin polymers such as ZEONEX® (based ondicyclopentadiene) manufactured by Nippon Zeon Company; and amorphouscyclo-olefin copolymers such as APEL™ manufactured by Mitsui. Anothersuitable polymer for the second substrate is polysulfone. Secondsubstrate 16 should maintain its “in-band” optical properties over anextended period of time. The term “in-band” optical properties shallmean those optical properties that affect or substantially influenceradiation at wavelengths emitted by the radiation emitters within theassembly. Specifically, it should maintain an absence of opticalabsorption (particularly, at the wavelength emitted by radiation sourceswithin the assembly), be resistant to hazing and scattering, and beresistant to reactions that cause it to turn yellow or other color overtime in such a manner as to unintentionally absorb significant portionsof radiation emitted by light sources within the assembly. In manyembodiments, second substrate 16 should be resistant to degradation uponprolonged, repeated or intense exposure to short-wavelength radiationsuch as blue, violet or UV light or upon exposure to ambient heat, heatfrom processing the assembly or from internal heat generated byoperating the assembly. For embodiments of the present inventioncontaining emitters of blue-green, blue, violet or UV light, it may beespecially important for the second substrate 16 to start and remainsubstantially transparent in the short wavelength bands emitted,avoiding the yellowing phenomena typical of some transparent polymermaterials, and thus avoiding excessive tendencies toward increasedabsorption of radiation produced by those emitters. Second substrate 16may also be treated with a coating (not shown), such as ananti-reflection coating, a barrier coating or other thin-film coating,on one or more of its surfaces. Such a coating may be employed, forexample to enhance extraction efficiency for optical radiation emittedby sources within the chamber 21 and exiting through surfaces of secondsubstrate 16. Another coating may be used to prevent permeation ofoxygen, water vapor or other agents through second substrate 16 into thechamber 21, to prevent impurities from leaching out of second substrate16 into liquid 20, or to prevent portions of liquid 20 from permeatinginto or reacting with second substrate 16.

Second substrate 16 is generally semi-rigid to rigid, however it may beadvantageous in some embodiments for second substrate 16 to be madesubstantially flexible. By making second substrate 16 flexible, it maybe possible to accommodate bulk thermal expansion of liquid 20 as mayoccur during prolonged operation of the assembly at high power levels,or during operation in environments having an ambient temperaturegreater than that prevailing during the manufacture of the assembly.Such flexibility may be accomplished by utilizing thinner sheets oftransparent material for construction of second substrate 16 or bychoosing more flexible materials to begin with. Alternately, secondsubstrate 16 may be made flexible by increasing the area of the chamber21 in such a way that portions of second substrate 16 are disposed atconsiderable distance from retaining forces applied by seal 18 (or byother mechanisms in the vicinity of seal 18).

As shown in FIGS. 1–3, assembly 10 further includes a seal (or gasket)18 extending between first and second substrates 14 and 16 so as todefine a closed region therebetween that is hereinafter referred to as a“sealed chamber.” As used herein, the term “chamber” may include acavity or similar structure. The seal or gasket 18 is preferably made ofepoxy, butyl rubber, a frit of metallic and/or glassy composition,ceramic, metal alloys such as solder, or other relatively inert barriermaterial. Within the sealed chamber is a liquid, gel, or other materialthat is either moderate to highly thermally conductive, moderate tohighly convective, or both. As used herein, a “gel” is a medium having asolid structure and a liquid permeating the solid structure. Because agel includes a liquid, the term liquid is used hereinafter to refer toliquids contained in gels as well as non-gelled liquids.

The liquid 20 is disposed within the sealed chamber 21 so as to surroundeach of the LED chips 12 used in the device. Enough liquid 20 may bedisposed within the sealed chamber 21 such that the sealed chamber 21 iseffectively filled. Alternately, the volume of liquid 20 used may beless than the volume of the sealed chamber 21 such that a portion of thesealed chamber 21 remains occupied by a bubble of air, gas or vacuum(not shown). Such an unfilled portion of the chamber 21 may be usefulfor accommodating thermal expansion of the liquid 20 or as a visualindication that the remainder of the chamber 21 is filled. More than onetype of liquid 20 may also be used within the same sealed chamber 21such that more than one zone is defined (not shown), and occupied by asuch liquids if they are not miscible. Such a configuration may beuseful if different physical, optical or chemical properties are desiredfor the liquid 20 present in different portions of the chamber 21.Liquid 20 is preferably, but not necessarily, electricallynonconductive. The materials utilized for substrates 14 and 16, seal 18,and LED chips 12 preferably are selected such that they do not react orotherwise ionize the liquid 20 so as to cause the liquid to becomesignificantly electrically conductive. High electrical conductivity ofliquid 20 could create a short circuit across the LED chips 12 dependingupon how they are disposed in the sealed chamber 21. Preferably, liquid20 has low to moderate thermal expansion, or a thermal expansion thatsubstantially matches that of first substrate 14, second substrates 16,or seal 18, and in some embodiments, a slightly higher thermal expansionmay be desired to increase convection while in other embodiments, a lowcoefficient of thermal expansion may be desired to minimize stress onthe optional die attach (not shown), optional solder bumps (25) and seal18. Liquid 20 is also preferably inert and does not readily decompose orotherwise react with external agents that manage to enter the sealedchamber 21 over time or with impurities contained within the sealedchamber 21 from the time of manufacture. Liquid 20 should also maintainits optical properties over time. Specifically, it should be resistantto reactions that cause the liquid to turn yellow or other color overtime in such a manner as to unintentionally absorb significant portionsof radiation emitted by light sources within the assembly. Forapplications where the assembly will be exposed to short wavelengthradiation such as UV, violet, blue or blue-green optical radiation fromthe ambient environment or from emitters within the assembly, liquid 20should be resistant to degradation upon prolonged, repeated or intenseexposure such radiation. For embodiments of the present inventioncontaining emitters of blue-green, blue, violet or UV light, it may beespecially important for the liquid 20 to remain substantiallycolorless, avoiding excessive tendencies toward increased absorption ofradiation produced by those emitters. Liquid 20 should also becompatible with the seal material. The liquid should also besubstantially transparent to some or all of the wavelengths of radiationemitted from the radiation emitters 12. It will be appreciated however,that liquids may be selected or dyes may be utilized to selectivelyfilter the radiation emitted from the radiation emitters 12. Liquid 20also preferably has an index of refraction between that of the radiationemitters 12 and the glass or otherwise have an index that approximatelymatches one of the emitters or the glass. Another benefit that mayresult from providing liquid 20 in contact with emitters 12 and anyoptional wire bond, is that the liquid provides viscous damping of anyvibration of the wire bond. Additionally, liquid 20 (also referred toherein as an intermediary material that is disposed between theemitter(s) and the second substrate or protective barrier) may provideincreased optical extraction efficiency by minimizing internalreflection within the device. In this respect, it should be noted thatmost LED chip materials possess high refractive indices, such thatgreater light extraction losses occur by total internal reflection andinternal absorption when such chips are surrounded by media with verylow refractive indices. Air or other atmospheric gasses typically have arefractive index near 1.0 such that a configuration involvingjuxtaposition of LED chips directly against air leads to poor opticalcoupling. For this reason, liquid 20 is selected to have a relativelyhigher refractive index, consistent with other functional requirements.The refractive index of liquid 20 at the emission wavelength of sourceswithin the assembly is generally higher than about 1.3, but is morepreferably higher than 1.4 and in some cases may be higher than 1.5.With addition of small-particle fillers or other additives, liquid 20may become a suspension or solution with an effective refractive indexas high as 2.5. Such additives may include inorganic fillers or organicmaterials, including nanoparticles, doped nanocrystals, conventionalphosphors. Certain types of optical fluids such as oils may also beavailable with or without such fillers or additives and having elevatedrefractive indices greater than 1.4 and as high as 3.0. Liquid 20 may bepropylene carbonate or another liquid or gel having one or more of theabove described properties. One commercially available liquid that maybe used is Galden® D02TS available from Montedison S.P.A. of Milan,Italy.

The liquid 20 may be dispensed within the sealed chamber 21 by vacuumback-filling or other conventional techniques such as those used todispense an electrochromic solution between two glass substrates whenmaking an electrochromic mirror or window. One or more fill holes may beprovided in either the seal or in one or both of the substrates. Afterthe sealed chamber 21 is filled with liquid 20, the hole(s) may beplugged with a UV-curable or other plug material.

In the embodiment shown in FIGS. 1–3, the substrates are approximatelyone inch by one and one quarter inch rectangles. The size of thesubstrates may, however, be much bigger and be as large as anarchitectural window or the like, or may be smaller depending on theapplication. Preferably, the volume of liquid in the sealed chamber 21defined by the seal and the two substrates is more than about 20 timesgreater than the volume of the radiation emitters to ensure sufficientheat transport. In some embodiments, it may be possible to reduce thisvolume as low as 2 times the volume of the radiation emitters. Althoughsubstrates 14 and 16 are depicted in FIGS. 1 and 2 as being rectangular,it will be appreciated that the substrates may have virtually any shape.Square, circular, hexagonal and octagonal shapes may be desirable inspecific applications. Seal 18 need not be formed in the same shape asthat of the substrates. Seal 18 serves to bond the two substratestogether and form sides of the sealed chamber 21 in which liquid 20 iscontained. Seal 18 should also serve as an environmental barrier so asto impede diffusion of water, oxygen, and other substances into thesealed chamber 21 while also impeding liquid 20 from exiting the sealedchamber 21. Seal 18 may also function as a spacer for maintaining theseparation distance of substrates 14 and 16. Spacers (not shown) in theform of pillars, glass beads, etc. disposed between the substrates maybe used as the sole means for maintaining the separation distance ofsubstrates 14 and 16 or as a supplement to the spacing function servedby the seal. The radiation emitters or other electrical components inthe sealed chamber 21 (described further below) may also provide thisspacing function.

To enable electrical current to flow to and through anyelectroluminescent radiation emitters 12 that may be present in thesealed chamber 21, electrical conductors are provided that areelectrically coupled to emitters 12 and extend out from the sealedchamber 21. When an electrically conductive first substrate 14 isutilized, the negative or positive terminal of the emitters 12 may bedirectly mounted to first substrate 14 while the other of the terminalof emitters 12 may be soldered (note solder bumps 25) or otherwiseelectrically connected to a conductor 22 provided on the bottom innersurface of second substrate 16. Conductor 22 may be made of metal ormade of indium tin oxide (ITO), which is a common transparent conductor.With such a configuration, the spacing between first substrate 14 andsecond substrate 16 would be approximately equal to the thickness ofemitters 12, which is typically on the order of 0.012 inch, but may beas low as 0.001 inch or as high as 0.500 inch. In this embodiment,partial conductivity of liquid 20 may supplement or serve as thereplacement for solder bumps 25 at the top of the emitters 12 makingelectrical connection to conductor(s) 22 on second substrate 16.

As shown in FIG. 2, electrical leads 26 and 30 may be coupled toelectrical conductor 22 and first substrate 14 by respective conductiveclips 24 and 28. Such clips may have a construction similar to thoseutilized in electrochromic devices. An example of suitable clips isdisclosed in U.S. Pat. No. 6,064,509 entitled “CLIP FOR USE WITHTRANSPARENT CONDUCTIVE ELECTRODES IN ELECTROCHROMIC DEVICES” filed onAug. 22, 1997, by William L. Tonar et al. Additionally, two pairs oflead posts 31 may extend from opposite ends of clips 24 and 28 so as tofunction as leads 26 and 30. Such lead posts would allow the package tobe mounted to through-holes in a printed circuit board.

While first substrate 14 is shown as a flat plate, it will beappreciated by those skilled in the art that substrate 14 may includerecesses, protrusions, fins, etc. to increase the exterior surface areaand maximize its effectiveness as a heat sink. For example, a heat sinksuch as that currently employed on Pentium or Athlon® CPU chips may beused. Additionally or alternatively, a fan, forced convection system, orPeltier type cooling system may be used to increase the dissipation ofheat from the assembly. For example, a Peltier type cooling structuremay be used optionally comprising a Peltier cooler 33, heat sink 35,and/or fan 37 attached to the backside of first substrate 14, as shownin FIG. 3B, or otherwise made integral with first substrate 14. Otherthermoelectric cooling materials, structures or means may also besubstituted for the Peltier cooling structure in this configuration. Asdescribed further below, at least one electrical component 31 may beprovided in the sealed chamber 21 along with emitter(s) 12.

Furthermore, substrate 14 may include cup-shaped recesses on its uppersurface with one such recess for each radiation emitter 12 provided inthe device. Provided substrate 14 has a reflective upper surface, suchrecessed cups would serve to redirect light emitted from the sides ofthe emitters in a forward direction through second substrate 16.Alternatively, if substrate 14 is not otherwise reflective, the topsurface may be coated with a reflective material particularly withinsuch recessed cups or a reflective pad may be located under theemitters. Such a reflective pad may be the electrical conductor, when anonconductive first substrate is employed.

Similarly, second substrate 16 need not have a flat upper or lowersurface. Substrate 16 may include integral microlenses, diffusers, orthe like. Additionally, graphic masks, appliques, or color filters maybe applied to, or made integral with, one or more of the surfaces ofsecond substrate 16. For example, an applique may be applied that allowslight emitted from the emitters to be transmitted through letters of asign, such as an exit sign. In this manner a high brightness, back-litdisplay panel may be provided. The panel may be static (e.g., facia,applique, screen-printed mask, etc.) or dynamic (e.g., a liquid crystaldisplay (LCD) panel). When an LCD panel is used as second substrate 16,or otherwise attached to or mounted proximate substrate 16, it ispreferred, but not essential, that the radiation emitting device includered, green, and blue (RGB) LEDs or alternatively binary complementarywhite emission source combination or an InGaN LED/fluorescent whiteemitting source combination, to enable a dynamic full-color display.

As illustrated in the drawing figures, the radiation emitting assemblymay include one or more emitters 12. Radiation emitters 12 may emitlight within the same wavelength bands or may emit light in differentwavelength bands. For example, one or more LEDs may emit IR or UVradiation, while the others emit visible radiation. As another example,the radiation emitters may emit light of complementary colors such thatthe light emitted from radiation emitters 12 overlaps and forms whitelight or light of a color that is not otherwise emitted from any of theradiation emitters individually. To produce white light or almost anyother color of illumination, three radiation emitters may be used withone emitting red light, another emitting blue light, and the thirdemitting green light. Alternatively, two radiation emitters may be usedthat emit binary complementary colors to produce effective white lightin the manner disclosed in commonly assigned U.S. Pat. No. 5,803,579,entitled “ILLUMINATOR ASSEMBLY INCORPORATING LIGHT EMITTING DIODES,” byRobert R. Turnbull et al.

When more than one radiation emitters 12 that are electroluminescent areutilized in the inventive device, separate conductive leads may beprovided to each electroluminescent emitter 12 so that the emitters maybe independently activated and their intensities independentlycontrolled. For example, rather than utilizing a single transparentconductive layer 22 across the entire surface of second substrate 16 inthe embodiment shown in FIGS. 1–3, the transparent conductive layer 22may be etched or otherwise patterned so as to provide discreteconnections to the top, normally positive, terminals of emitters 12.Such an example is shown in FIG. 3C where the conductive layer ispatterned to form two discrete connections 22 a and 22 b. In this case,two separate and smaller clips (not shown) may be used in place of clip24 (FIG. 2). Conversely, if first substrate 14 is made of anelectrically nonconductive material, as in the embodiments describedbelow and shown in FIGS. 4, 5, 6A, 6B, 10, 11, and 18 separateelectrically conductive traces may be formed on the first substrate toprovide discrete connections to the positive and/or negative terminalsof emitters 12.

In the event it is desired to have the inventive radiation device emitwhite light or other colored light with a hue differing from that oflight emitted by enclosed electroluminescent emitters 12, it may bedesirable to incorporate a photoluminescent radiation source such as aphosphorescent or fluorescent material into substrate 16 or in a layeron substrate 16. Alternatively, a photoluminescent source may be appliedas one or more blobs over an electroluminescent emitter 12, or may bedissolved or suspended in liquid 20. Photoluminescent sources could beused to enable the assembly to emit substantially white light when thephotoluminescent source is irradiated by the radiation emitted fromelectroluminescent emitters 12. Photoluminescent sources could also beused to generate green, blue-green, amber, orange, or red light whenirradiated by UV, violet, or blue emitting electroluminescent emitters12. An example of the use of photoluminescent sources in this manner isdisclosed in commonly assigned U.S. patent application Ser. No.09/723,675, entitled “LIGHT EMIT G ASSEMBLY,” and filed on Nov. 28, 2000by John K. Roberts et al.

A photoluminescent source may additionally or alternatively bedispersed, dissolved, or suspended in liquid 20. The convection ofliquid 20 may tend to keep the photoluminescent material in suspensionor in solution. Such dispersal of photoluminescent media within theliquid 20 may also help maintain uniformity of color and/or luminance ofthe device and may help limit degradation of the photoluminescent mediawith long term use.

While liquid 20 has been described above as preferably beingelectrically nonconductive, liquid 20 may nevertheless be conductiveprovided that the resistance of liquid 20 is greater than that betweenthe negative and positive terminals of the radiation emitters 12 in thechamber 21 and that the resistive path through the liquid between theelectrical conductors is much greater than the resistive path throughthe liquid between each electrical conductors and the negative orpositive terminals to which they are respectively coupled. Conceivably,by using a conductive liquid, the need for a wire bond or solder may beeliminated by allowing current to flow to an electroluminescent emitter12 from first substrate 14 or second substrate 16 via a thin portion ofliquid 20.

Additionally, additives such as anti-oxidants or UV stabilizers may beadded to liquid 20 to improve system life. Electrolytes can be carefullyadded in small quantities to establish any optional electricalconductivity desired.

FIG. 4 shows a radiation emitting device 40 constructed in accordancewith a second embodiment of the present invention. As shown, radiationemitting device 40 includes an electrically nonconductive firstsubstrate 32, a second substrate 16, and a seal 18 disposed between thetwo substrates to define a sealed chamber 21 in which a liquid or gel 20is contained. Device 40 further includes a first electrical trace 34 anda second electrical trace 36 provided on the upper surface of firstsubstrate 32. As shown in FIG. 4, two radiation emitters 12 are mountedon first electrical trace 34 with their cathodes in electrical contactwith trace 34. Trace 34 extends outward from the sealed chamber 21 so asto enable electrical contact with an external device. Second trace 36also extends from within the sealed chamber and is electrically coupledto wire bonds 38 that are coupled to the negative or positive terminalsof radiation emitters 12. As suggested above, both radiation emitters 12may share common electrical traces or may have discrete traces forallowing for independent activation and control.

First substrate 32 may be made of alumina or other ceramic substrate,such as beryllia ceramic, passivated metals, metal clad or metal coreprinted circuit board, passivated, anodized, or laminated metal printedcircuit board, or may be made of glass, an epoxy sheet, or an aliphaticor olefinic plastic such as those discussed above. If both the first andsecond substrates are made of plastic, it may be possible to configureand join the two substrates without requiring a seal or other spacers.Commonly-assigned U.S. Pat. No. 6,193,379, entitled “ELECTROCHROMICASSEMBLY INCLUDING AT LEAST ONE POLYMERIC SUBSTRATE,” filed on Jun. 9,2000, discloses various plastic materials and structures for formingsealed chambers when used for containing an electrochromic medium. Suchdisclosed structures may be used in the light emitting assembly of thepresent invention.

Device 40 may further include a micro-groove lens 41, which may be aFresnel lens, a diffraction grating, total internal reflection (TIR)lens, catadioptric lens, kinoform lens, a holographic optical element(HOE), or other optical lens. Lens 41 may be integrally formed on eitherthe inside or outside surface of second substrate 16 or may be opticallycoupled to second substrate 16. A suitable micro-groove lens isdisclosed in commonly assigned U.S. Provisional Patent Application No.60/270,054 entitled “RADIATION EMITTER DEVICE HAVING A MICRO-GROOVELENS,” filed on Feb. 19, 2001 by John K. Roberts.

FIG. 5 shows a radiation emitting device 50 constructed in accordancewith a third embodiment of the present invention. Like device 40 of thesecond embodiment, device 50 utilizes an electrically nonconductivefirst substrate 32 that is spaced apart from a second substrate 16 by aseal 18 that forms a sealed chamber 21 in which a liquid or gel 20 iscontained. Device 50 differs from device 40 in that a lateral-type LED52 with two top-side electrode contacts is utilized. LED 52 may bedirectly mounted on substrate 32 within a gap formed between a firstelectrical trace 54 and a second electrical trace 56 that are providedon the upper surface of substrate 32. As in the second embodiment,electrical traces 54 and 56 extend from within the sealed chamber 21 tothe exterior of the device to allow for an electrical signal to beapplied to LED chip 52 from the exterior of device 50. First trace 54 isprovided to be coupled to a first wire bond 58 that is coupled to theanode of LED chip 52. Second trace 56 is provided for coupling to asecond wire bond 60 that is coupled to the cathode of LED chip 52.

Both the embodiments shown in FIGS. 4 and 5 utilize electrical tracewires that are bonded to one of the contact terminals of the radiationemitters. Preferably, the trace wires are flat ribbon wires having arectangular cross section and are bonded to the contact terminal of theradiation emitter using a wedge bond. Such a wire and bond reduce thespacing needed to accommodate the radiation emitters between thesubstrates since they provide a lower profile bond than a conventionalwire having a circular cross section that is bonded using a ball-shapedbond. However, in some embodiments, conventional circular bond wire maybe used, and in other embodiments, none may be necessary.

FIGS. 6A and 6B show two variations of a fourth embodiment of thepresent invention whereby irregularly shaped substrates are used to formthe sealed chamber 21. Specifically, in FIG. 6A, a structure is shown inwhich the back and at least part of the sides of the sealed chamber 21are defined by an irregularly-shaped substrate 70, which may betransparent, partially transparent or opaque, and may be made of metalor plastic. Substrate 70 includes an opening 71 that lies aboveradiation emitter(s) 12. As illustrated, a window substrate 72 that issubstantially transparent to the radiation emitted from radiationemitters 12, is secured to substrate 70 across opening 71. A seal orgasket 74 may be disposed between window substrate 72 andirregularly-shaped substrate 70 to seal the chamber 21.

In FIG. 6B, a structure is shown in which an irregularly shapedtransparent second substrate 75 is provided to define the front and atleast a portion of the sides of the sealed chamber 21. Second substrate75 may be ultrasonically welded or otherwise bonded to first substrate32 in order to seal the chamber 21. As illustrated, second substrate hasa dome-like shape and includes a peripheral shoulder 76 and rim 77 forengaging the edges of first substrate 32. Electrical connections toradiation emitter(s) 12 may extend through vias formed in firstsubstrate 32 that extend from an inner surface to an outer surfacethereof. The chamber 21 may be filled with the second substrate invertedand prior to ultrasonic welding. Alternatively, a fill hole may beprovided through first substrate so that the chamber may be filled afterwelding. A UV curable or other plug may then be used to seal the fillhole.

FIG. 7 shows a fifth embodiment of the present invention. In this fifthembodiment, a reflective mask 80 is provided on a surface of secondsubstrate 16. The reflective mask 80 includes a plurality of non-maskedopenings 82 above each radiation emitter 12. Mask 80 may optionallyinclude a small reflective spot 84 directly over each emitter 12 so asto prevent light from directly emitting from an emitter 12 through mask80. In this manner, emitters that emit light of different colors may bedisposed within the chamber 21, and the light emitted from the emitterswill mix within the chamber 21 prior to being emitted from the assembly.Mask 80 may be a patterned reflective or diffuse coating or a filter andbe made integral with patterned conductors if used. Patterns other thanthose shown may be used to optimize various optical qualities withoutdeparting from the scope of the invention.

FIGS. 15 and 16 show yet another embodiment of the present invention. Asshown in the cross-sectional view of FIG. 15, radiation emitted fromemitters 12 is either nearly completely transmitted, partiallytransmitted and partially internally reflected, or nearly completelyinternally reflected from second substrate 16 depending upon the angleat which the radiation strikes the surfaces of second substrate 16.Whether radiation (i.e., a light ray) is internally reflected dependsupon whether the light ray strikes the surface at an angle that isgreater than the critical angle as determined by application ofFresnel's equations and Snell's Laws. If the entire upper surface offirst substrate 14 served as a specular reflector, those light rays Tthat are totally internally reflected from a surface of second substrate16 would continue to be totally internally reflected from the uppersurface of first substrate 14 and then again from the surfaces of secondsubstrate 16. To cause the light rays T that would otherwise be totallyinternally reflected, to ultimately exit through the second substrate ofthe radiation emitting device, upper surface of first substrate 14 mayhave different reflective zones—namely, a specularly reflective zone 301and a diffuse reflective zone 303. As shown in FIGS. 15 and 16, separatespecularly reflective zones 301 are provided for each emitter 12 and arecircular in shape with the associated emitter 12 disposed in the centerof the circle. The remainder of the upper surface of first substrate 14(with the exception of that area covered by electrical traces andcontact terminals) constitutes the diffuse reflective zone 303. Specularreflective zones 301 may be provided as a portion of the patternedelectrical conductor traces 304. As will be apparent to those skilled inthe art, the diameter of the circular specular reflection zone 301 isselected to be small enough not to reflect light rays that are totallyinternally reflected from a surface of the second substrate 16, and yetlarge enough to reflect all other light. The diffuse reflective zone 303is provided to diffuse those light rays T that are totally internallyreflected from a surface of the second substrate 16 and thereby reflectthe light at angles that are likely to allow the light to exit thesecond substrate 16. Diffusely reflective zone 303 may have a coatingincluding a photoluminescent material.

While specular reflection zones 301 are shown as being circular on aplanar surface, it will be appreciated that the first substrate 14 mayinclude recessed reflective cups. FIGS. 17A and 17B show alternatevariations of such a construction. Specifically, FIG. 17A shows the useof reflective partitions 311 between radiation emitters 12 so as todivert those light rays that would otherwise strike a surface of secondsubstrate 16 at an angle exceeding the critical angle. Reflectivepartitions may form a parabolic reflective cup or other shaped cup andmay be specular or diffuse in surface character. FIG. 17B shows avariation of the structure shown in FIG. 17A in which reflectivepartitions 313 are integrally formed in the upper surface of firstsubstrate 315. Note that partitions 311 and 313 in the above embodimentsmay function as a spacer between the first and second substrates.

FIG. 8 shows a vehicle headlamp 2600 constructed in accordance with thepresent invention. As shown, the headlamp includes a light emittingassembly similar to those shown above, except that it includes an arrayof radiation emitters 2603 and 2605 within the sealed chamber 21 that isformed between a first substrate 2601, a second substrate 2630, and aseal (not shown). Second substrate 2630 preferably includes a pluralityof micro-lenses 2631 formed in its outer surface above each one or eachgroup of emitters 2603, 2605. First substrate 2601 preferably includes aheat extraction member 2621 and a plurality of reflective cups 2602 inwhich each one or each group of emitters is mounted. Emitters 2603 areconnected to electrical conductor strip 2607 through a wire bond 2609and a resistor 2611. Emitters 2605 are connected to electrical conductorstrip 2613 through a bonding wire 2615 and a resistor 2617. A secondassembly similar to that shown in FIG. 8 may also be disposed in acommon headlamp housing and preferably disposed at an angle relative tothe first assembly so as to produce high beams. By utilizing the highpower light emitting assembly of the present invention, vehicleheadlamps may be constructed that require fewer LEDs or other emittersto produce the requisite illumination levels that are expected forvehicles. Headlamp 2600 may also be a fog lamp or other lamp assembly.

FIG. 9 shows an exemplary circuit 100 that may be used in the aboveembodiments of the present invention. As shown, three externalconnections are provided including a ground contact 102, a first supplyvoltage contact 104, and a second supply voltage contact 106. The secondsupply voltage contact is provided to enable a bias voltage to beapplied between a first LED 110, and two second LEDs 112 via a resistor114, and thereby adjust the relative intensity of the second LEDsrelative to the first LED, which is particularly advantageous when thefirst and second LEDs emit light of different colors. A resistor 118 iscoupled between the first LED and first supply voltage contact. Resistor118, first LED 110, and second LEDs 112 are coupled in series betweenfirst supply voltage contact 104 and ground contact 102. As shown inFIG. 9, a plurality of such series-connected LEDs may be connected inparallel. Portions of circuit 100 may be printed on one or both ofsubstrates 14 and 16. Portions of circuit 100 may be disposed inside oroutside of the sealed chamber 21, with contacts 102, 104, and 106extending out of the chamber for external connection. Resistors 114 and118 may likewise be provided outside of the chamber to lower the heatgenerated inside the chamber.

In a preferred embodiment, LEDs 110 emit blue-green light while LEDs 112emit amber light. With such an arrangement, effective white light may beemitted from the assembly.

FIG. 10 shows an initial subassembly that forms a part of the finalassembly shown in FIG. 11 in accordance with a sixth embodiment of thepresent invention. The package 150 includes a printed circuit board 155,which in the example provided below, is made of BeO. Variouselectrically conductive traces are formed on circuit board 155.

In the example shown in FIGS. 10 and 11, a first trace 160 extends froma first electrical contact 162 to a first terminal of each of four firstresistors 164 a–164 d. Traces 166 a–166 b extend from a second terminalof respective resistors 164 a–164 d to a respective anode of acorresponding pad 168 a–168 d upon which is mounted a first set of LEDs170 a–170 d. First LEDs 170 a–170 d are mounted with their anode inelectrical contact with pads 168 a–168 d, respectively. Traces 166 a–166d also extend to a position proximate pads 172 a–172 d upon which aremounted respective second LEDs 174 a–174 d. Second LEDs are mounted withtheir anodes in electrical contact with pads 172 a–172 d. Wire bonds 176a–176 d electrically couple the cathodes of second LEDs 174 a–174 d tothe end of trace 166.

The cathodes of first LEDs 170 a–170 d are electrically coupled viacorresponding wire bonds 178 a–178 d to a respective trace 180 a–180 d,which in turn are coupled to respective first terminals of secondresistors 182 a–182 d. Second terminals of resistors 182 a–182 d, inturn, are commonly coupled to a trace 184, which extends and iselectrically coupled to a second contact terminal 186. The resistors 164a–164 d and 182 a–182 d are preferably 2Ω, 1 W thick film resistors thatare printed on circuit board 155.

Pads 172 a–172 d, to which the anodes of second LEDs 174 a–174 d arerespectively coupled, are electrically coupled to respective traces 188a–188 d. Each of these traces 188 a–188 d is connected by means of arespective wire bond 190 a–190 d to another respective trace 192 a–192 don the opposite side of trace 184. Traces 192 a–192 d are respectivelycoupled to cathodes of respective third LEDs 194 a–194 d by a wire bond196 a–196 d. The anodes of third LEDs 194 a–194 d are mounted oncorresponding pads 198 a–198 d, which in turn are commonly coupledtogether via a trace 200 that extends and is electrically coupled to athird contact terminal 202.

With the circuit layout as shown in FIG. 10, the resulting circuit has aschematic corresponding generally to FIG. 9, where first LEDs 170 a–170d correspond to LEDs 110, second and third LEDs 174 a–174 d and 194a–194 d correspond to LEDs 112, first resistors 164 a–164 d correspondto resistors 114, and second resistors 182 a–182 d correspond toresistors 118.

In a preferred embodiment and in the example discussed below, first LEDs170 a–170 d are preferably InGaN LED chips that emit blue-green light.Both the second and third LEDs 174 a–174 d and 194 a–194 d are AlInGaPLED chips that emit amber light. By utilizing these LED chips, effectivewhite light may be emitted from the package in accordance with theteachings of U.S. Pat. No. 5,803,579 entitled “ILLUMINATOR ASSEMBLYINCORPORATING LIGHT EMITTING DIODES” by Robert R. Turnbull et al.

Once the above-described circuit has been constructed, a cover glass 205is attached to circuit board 155 with an epoxy seal 210, which encirclesthe circuit components, with the exception of electrical contacts 162,186, and 202 and with the exception of a small hole through which theresultant sealed chamber 21 may be filled with a liquid or gel. In theexample discussed below, the seal chamber was filled with Galden® D02TS.Subsequently, the hole provided in the epoxy between cover 205 andcircuit board 155 was plugged with a plug 212 made of Dynax UV cureadhesive. The resultant structure is shown in FIG. 11.

As apparent from FIG. 11, the resultant final package assembly includesthree contact pads 162, 186, and 202, which extend outward from thesealed chamber 21 and up to the edge of printed circuit board 155. Inthis manner, a conventional low insertion force edge connector may beconnected to the contact pads for coupling to the drive circuit. Such anedge connector may be a conventional PCI or ISA slot connector. Itshould be understood that another number of contact pads may be used,dependent on the electrical configuration used.

The invention will be further clarified by the following example, whichis intended to be exemplary of the invention and are not intended in anymanner to limit the invention.

EXAMPLE

To demonstrate the effectiveness of the present invention, a packageassembly was constructed as illustrated in FIGS. 10 and 11 and describedabove. The structure had a length of approximately 1.5 inches and awidth of approximately 1.5 inches, with the external contact pads beingapproximately 0.25 inch long. To demonstrate the effectiveness of thepresent invention, the illumination from the device was measured atvarious power levels prior to filling the sealed chamber 21 with anyliquid. Then, the assembly was filled with liquid and plugged and theilluminance was again measured at the same power levels. The results ofthese measurements are illustrated in FIG. 12, with the illuminancemeasured in foot-candles at 18 inches. As apparent from FIG. 12, theprovision of the liquid in physical and thermal contact with the LEDsimproved their performance markedly. The improvement increased as theapplied power increased. It should be understood that, for this sample,increased illuminance at each indicated power level for the filledradiation emitter relative to the unfilled radiation emitter is anindication of reduced junction operating temperature and reducedassembly thermal resistance.

FIG. 13 is a plot of the relative spectral irradiance as a function ofwavelength with the chamber 21 of the device not filled with any liquid.The relative spectral irradiance was measured at five different powerlevels. Subsequently, after the device was filled with liquid, the sameplots were obtained and are illustrated in FIG. 14.

While the above invention has been described with respect to theprovision of optical radiation emitters and other radiation emittingdevices within a sealed chamber 21 of the inventive package, theinventive package may similarly be used to improve the heat dissipationfrom other electronic components. For example, as shown in FIG. 18, amicroprocessor 230, a sensor 240, a resistor 245, and other electroniccomponents, particularly other semiconductor electronic components, maybe disposed within sealed chamber 250 that is formed between two members255 and 260. Examples of other electronic components that coulddesirably be placed in the sealed chamber either alone or in combinationwith radiation emitters, microprocessors, resistors, sensors or othercomponents, including thermistors, diodes, Zener diodes, photodiodes,transistors, voltage regulators, Peltier effect diodes or otherthermoelectric cooling chips or materials, phototransistors, etc.Members 255 and 260 may have any of the constructions discussed above.However, if none of the components within the sealed chamber are opticalcomponents, both members 255 and 260 may be opaque. Without such aconstraint, first member 255 may, for example, be a printed circuitboard while second member 260 may be a heat sink, preferably made of ahighly thermally conductive material and having a large surface area.Such a large surface area may be provided by including various fins 262extending outward away from the sealed chamber. As also shown in FIG.18, various passageways 264 may be provided through heat sink member 260through which liquid may flow. These passages may join into sealedchamber 250 to allow the liquid contained therein to flow through thepassageways to expedite heat dissipation from the liquid.

The electronic components mounted in the chamber may be surface mount(SMT), through-hole (THD), ball grid array (BGA), chip-on-board,chip-on-glass, or other common semiconductor device form. Electricalconnections to/from/between these components, and any patternedconductors within the chamber or to contacts exiting the chamber, may besolder, solder bump, solder paste, conductive epoxy, eutectic attach,wire bond, leadframe, or other electrical connection means.

Another alternative embodiment would enable both members 255 and 260 tobe printed circuit boards that are sandwiched together by an epoxy sealand filled with a liquid or gel. This may enable heat dissipation inaccordance with the present invention from circuit components mounted toeither or both of the circuit boards.

It should also be appreciated that the components shown in FIG. 18 maybe combined with a radiation emitter as in the other embodiments withina single sealed chamber. It may, for example, be beneficial to includeresistors and/or a sensor within the same sealed chamber as theradiation emitters. Such a sensor may be a thermal sensor, such as athermistor, so as to provide a mechanism for monitoring the temperatureof the liquid within the sealed chamber and for enabling the currentprovided to the LED chips to be controlled as a function of thetemperature within the chamber. This would allow the LED chips to bedriven at their maximum safe level. It may also be desirable to includea voltage regulator to regulate the electrical drive signal to anyelectroluminescent radiation sources in the chamber. Additionally, itmay be desirable to include any one or combination of transistors,phototransistors, diodes, photodiodes, or Zener diodes in the sealedchamber.

It may further be desirable to dispose an optical sensor within the samesealed chamber as the radiation emitters. Commonly assigned U.S.Provisional Application No. 60/192,484, entitled “LAMP ASSEMBLYINCORPORATING OPTICAL FEEDBACK,” and filed on Mar. 27, 2000, by JosephS. Stam et al. and U.S. patent application Ser. No. 09/818,958 entitled“LAMP ASSEMBLY INCORPORATING OPTICAL FEEDBACK,” filed on Mar. 27, 2001by Joseph S. Stam et al. disclose the advantages of utilizing an opticalsensor in combination with a plurality of LED chips. Such sensors may beemployed for many purposes such as to provide feedback for the controlof electroluminescent emitters 12 in the device. In the event an opticalsensor is provided in the sealed chamber, it may be desirable toincorporate light absorbing materials within the sealed chamber so as toeffectively filter the light that reaches the sensor.

The radiation emitter device described herein can be used to provide anear IR night vision system for use in automobiles and otherapplications. A radiation emitter device is constructed as describedabove using IR LED die emitting radiation at a wavelength longer thanthe human eye can detect but still within the sensing capability of anelectronic image sensor. Preferably, this wavelength range is between800 and 880 nm, but may be as low as 700 nm or as high as 1200 nm. SuchIR-emitting LED die are available from Tyntec Corporation of Hsinchu,Taiwan.

Current vehicular night vision systems have several disadvantages whichare overcome by using a near IR night vision system. Current systemssense far IR radiation—essentially heat. Detectors which sense far IRradiation are significantly more expensive than detectors which sensenear IR radiation. Additionally, glass is opaque to far IR radiationthus mandating that the sensor be placed outside of the vehicle's cabinthereby subjecting the system to much harsher environmental conditions.Also, glass optics cannot be used and more expensive optical materialstransparent to far IR radiation must be used instead. Finally, objectswhich are not at a higher temperature than the ambient surroundings arenot sensed as well as hot objects. Therefore, it is possible to have anobject in the road which is not adequately detected by a far IR system.

The radiation emitter device of the current invention may thus beconfigured to emit radiation illuminating the scene imaged by thecamera. In an automobile, the IR illuminator assemblies may be packagedwith or near the vehicle's headlamps. Since IR radiation is notdetectable to the human eye, it is possible to substantially illuminatethe scene in front of a vehicle without any concern for glare disruptingoncoming or preceding drivers.

The camera is configured to image at least the same spectra of light asthe IR LEDs emit. Preferably, the camera's spectral sensitivity islimited by the use of filters to only the wavelength range of lightemitted by the IR LEDs. This reduces any washing-out or blooming in theimage from other light sources. The camera can be mounted to lookthrough the vehicle's windshield in the region cleaned by the vehicle'swiper and washer system by placing the camera in the mount of a rearviewmirror. The camera preferably uses a wide dynamic image sensor to allowfor imaging of both bright and faint objects in the forward scenesimultaneously. Such an image sensor is described in commonly-assignedU.S. Pat. No. 6,008,486 entitled “WIDE DYNAMIC RANGE OPTICAL SENSOR.”

If a scene rearward of the vehicle is to be imaged using such a near IRimaging system, the camera may be mounted in the center high-mountedstop lamp (CHMSL) in a tail light, or behind the rear window, while theradiation emitting device of the present invention may be mounted in thesame location as the camera or in a different one of the abovelocations. A similar rear vision system is disclosed in commonlyassigned PCT International Publication No. WO 00/15462, entitled“SYSTEMS AND COMPONENTS FOR ENHANCING REAR VISION FROM A VEHICLE,” byFrederick T. Bauer et al.

As will be appreciated by those skilled in the art, the radiationemitting device of the present invention allows for more efficientextraction of the heat generated by the radiation emitters. Thisimproved extraction allows for a greater driving current to be deliveredto the radiation emitters, which, in turn, generates higher radiationflux levels than previously obtained. The LED construction disclosed inthe commonly-assigned U.S. Pat. No. 6,335,548 discussed above, achievespower densities of up to about 2 W/in² or more while the structure ofthe present invention may obtain power densities of up to 5 to 10 W/in²or more. Certain embodiments of the present invention may be capable ofpower dissipation in excess of 1 W for miniature lamp applications(i.e., small area embodiments), and up to and exceeding 1000 W for highpower lamp applications (i.e., large area embodiments).

Additionally, the likelihood that any wire bonds utilized may fatigue orbreak is either eliminated (as in the case with the first embodimentwhere wire bonds are not required), or significantly reduced, since thepresent invention does not encapsulate these wire bonds with a solidencapsulant. Because the wire bonds used in the embodiment shown inFIGS. 4 and 5 are surrounded by a liquid or gel, shear forces cannot betransferred to the wire bond as a result of any thermal expansion orcontraction as would be the case if they were encapsulated in aconventional encapsulant material.

A manufacturing process for making embodiments of the present inventioncomprising light engine modules first includes mounting optional surfacemount, BGA, chips or other electronic components onto the firstsubstrate. Next, one or more LED chips to the first substrate usingeutectic attachment, solder attachment, die-attach adhesive, epoxy orthe like. Next, additional optional surface mount, BGA, chips or otherelectronic components may be mounted onto first substrate. A curingstage or reflow stage is typically performed, as appropriate to formpermanent electrical and mechanical bonds between chips and componentsand the first substrate. Next, wirebonding is performed for embodimentsusing wirebonds for electrical connection to one or more LED orelectronic component chip. Next, a barrier adhesive, seal or gasketmaterial is placed or dispensed onto first or second substrate. The sealmaterial can optionally or additionally be pre-arranged upon or madeintegral with portions of either first or second substrate. At any pointup to this point in the process, optional spacers may be placed withinthe region subsequently forming the cavity, either by placing ormounting them on the first substrate or the second substrate or bysandwiching them between the two substrates. Next, the first and secondsubstrates are placed in close proximity such that any seal material orstructure bridges the narrow gap between them along an appropriateportion of their surfaces. To facilitate large scale manufacturing andproduction of several modules at one time or modules having severalsemi-independent chambers, several first substrates may be placed ontoone second substrate (and associated seal material) or vice versa. Sealmaterial is next cured, sintered, or melted by thermal treatment orradiation exposure such as baking, IR heating, e-beam or microwavecuring, reflow or other similar process. Small openings may be leftwithin first or second substrate or seal material to provide a channelfor subsequent filling of the cavity. Fluid may then be introduced intothe cavity by vacuum-backfill process, 2-port pressure or gravityfilling or other means. After the cavity is filled, openings in thefirst or second substrate or seal may be plugged with UV curable epoxyor other sealant/barrier material.

The above description is considered that of the preferred embodimentsonly. Modifications of the invention will occur to those skilled in theart and to those who make or use the invention. Therefore, it isunderstood that the embodiments shown in the drawings and describedabove are merely for illustrative purposes and not intended to limit thescope of the invention, which is defined by the following claims asinterpreted according to the principles of patent law, including thedoctrine of equivalents.

1. An optical radiation emitting device comprising: a sealed chamber; afluid intermediary material contained in said sealed chamber and havinga refractive index greater than 1.0; an inorganic electroluminescentsemiconductor radiation emitter that emits optical radiation in responseto an electrical signal, said inorganic electroluminescent semiconductorradiation emitter disposed in said sealed chamber in physical andthermal contact with said fluid intermediary material; and first andsecond electrical conductors electrically coupled to said inorganicelectroluminescent semiconductor radiation emitter for energizing saidinorganic electroluminescent semiconductor radiation emitter.
 2. Theoptical radiation emitting device of claim 1, wherein said fluidintermediary material contained has a refractive index greater thanabout 1.3.
 3. The optical radiation emitting device of claim 1, whereinsaid fluid intermediary material contained has a refractive indexgreater than about 1.4.
 4. The optical radiation emitting device ofclaim 1, wherein said fluid intermediary medium is a liquid or gel. 5.The optical radiation emitting device of claim 1, wherein said deviceexhibits a power density of at least about 2 Watts/in².
 6. The opticalradiation emitting device of claim 5, wherein said device exhibits apower density of at least about 5 Watts/in².
 7. The optical radiationemitting device of claim 6, wherein said device exhibits a power densityof at least about 10 Watts/in².
 8. The optical radiation emitting deviceof claim 1, wherein said inorganic electroluminescent semiconductorradiation emitter is an LED chip.
 9. The optical radiation emittingdevice of claim 8, wherein said LED chip comprises one of the materialsincluded in the group consisting of AlInGaP, InGaAlP, GaN, InGaN,AlInGaN, AlGaAs, GaP, GaAsP, SiC and ZnSe.
 10. The optical radiationemitting device of claim 8 and further comprising a second LED chip. 11.The optical radiation emitting device of claim 10, wherein said LEDchips emit light of complementary colors that combine to form whitelight.
 12. The optical radiation emitting device of claim 1 and furthercomprising a photoluminescent emitter.
 13. The optical radiationemitting device of claim 12, wherein said inorganic electroluminescentsemiconductor radiation emitter and said photoluminescent emittergenerate radiation with distinctly different peak wavelengths from oneanother.
 14. The optical radiation emitting device of claim 13, whereinthe combined radiation generated by said inorganic electroluminescentsemiconductor radiation emitter and said photoluminescent emitter formwhite light.
 15. The optical radiation emitting device of claim 12,wherein said photoluminescent emitter comprises a material selected fromthe group consisting of fluorescent phosphor, fluorescent dye, andfluorescent crystal layer.
 16. The optical radiation emitting device ofclaim 12, wherein said photoluminescent emitter is in contact with saidinorganic electroluminescent semiconductor radiation emitter.
 17. Theoptical radiation emitting device of claim 12, wherein saidphotoluminescent emitter is in contact with a surface of said chamber.18. The optical radiation emitting device of claim 1, wherein saidinorganic electroluminescent semiconductor radiation emitter comprisesat least one electrode attached by means selected from the groupconsisting of: conductive epoxy die attach, eutectic die attach, solder,solder bump, and wire bond.
 19. The optical radiation emitting device ofclaim 1, wherein said inorganic electroluminescent semiconductorradiation emitter emits radiation with a peak wavelength in the visibleportion of the optical spectrum.
 20. The optical radiation emittingdevice of claim 1, wherein said inorganic electroluminescentsemiconductor radiation emitter emits radiation with a peak wavelengthin the UV portion of the optical spectrum.
 21. The optical radiationemitting device of claim 1, wherein said inorganic electroluminescentsemiconductor radiation emitter emits radiation with a peak wavelengthin the IR portion of the optical spectrum.
 22. An optical radiationemitting device comprising: a metallic substrate; a transparent coverattached to said metallic substrate to form a sealed chamber, saidtransparent cover comprising an integral lens; a fluid intermediarymaterial contained in said sealed chamber and having a refractive indexgreater than 1.0, said fluid intermediary material being substantiallyelectrically nonconductive; and an inorganic semiconductor radiationemitter mounted on a surface of said metallic substrate within saidsealed chamber in physical and thermal contact with said fluidintermediary material, said inorganic semiconductor radiation emitteremitting optical radiation through said lens in response to anelectrical signal.
 23. The optical radiation emitting device of claim 22and further comprising a heat sink in thermal contact with said metallicsubstrate.
 24. The optical radiation emitting device of claim 22,wherein said metallic substrate comprises a reflective cup formedtherein in which said inorganic semiconductor radiation emitter ismounted.
 25. The optical radiation emitting device of claim 22, whereinsaid inorganic semiconductor radiation emitter is an LED chip.
 26. Theoptical radiation emitting device of claim 22 and further comprising atleast one additional inorganic semiconductor radiation emitter mountedon a surface of said metallic substrate within said sealed chamber inphysical and thermal contact with said fluid intermediary material. 27.The optical radiation emitting device of claim 22 and further comprisingfirst and second electrodes electrically coupled to said inorganicsemiconductor radiation emitter for supplying an electrical signalthereto.